US4491800A - Switching circuit operable as an amplifier and a muting circuit - Google Patents

Switching circuit operable as an amplifier and a muting circuit Download PDF

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Publication number
US4491800A
US4491800A US06/499,703 US49970383A US4491800A US 4491800 A US4491800 A US 4491800A US 49970383 A US49970383 A US 49970383A US 4491800 A US4491800 A US 4491800A
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Prior art keywords
circuit
inverting input
input port
terminal
resistor
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Expired - Lifetime
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US06/499,703
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English (en)
Inventor
Shinji Miyata
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NEC Electronics Corp
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NEC Corp
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Assigned to NEC ELECTRONICS CORPORATION reassignment NEC ELECTRONICS CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: NEC CORPORATION
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/34—Muting amplifier when no signal is present or when only weak signals are present, or caused by the presence of noise signals, e.g. squelch systems
    • H03G3/341—Muting when no signals or only weak signals are present
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G1/00—Details of arrangements for controlling amplification
    • H03G1/04—Modifications of control circuit to reduce distortion caused by control
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G11/00—Limiting amplitude; Limiting rate of change of amplitude ; Clipping in general
    • H03G11/08—Limiting rate of change of amplitude
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/34—Muting amplifier when no signal is present or when only weak signals are present, or caused by the presence of noise signals, e.g. squelch systems

Definitions

  • the present invention relates to a switching circuit and, more particularly, to a switching circuit operable as an amplification circuit and a muting circuit.
  • a muting circuit finds its use in audio systems with a view to temporarily attenuating the signal level to be recorded or for attenuating the output thereof while no broadcast signal is received.
  • a conventional muting circuit which may generally be composed of an integrated circuit free of a capacitor, a portion of a signal path is grounded through a switch circuit made of a transistor or the like, so that a given signal is not transmitted from said portion.
  • the bias potential changes at the portion where the signal path is grounded to cause a clicking noise in the final output. Such clicking noise is also caused when the muted state is released, resulting in an unpleasant sound to the listener.
  • a principal object of the present invention is to provide a switching circuit suitable for switching between amplification and muting operations without causing an unpleasant noise.
  • a switching circuit operable as an amplifier and a muting circuit and which comprises: an amplifier having a non-inverting input port for receiving input signals, an inverting input port, and an output port; a first impedance element connected between said inverting input port and ground potential; a second impedance element and a third impedance element connected to the inverting input port of the amplifier; an output terminal; and switching means, whereby, for the amplification operation, the switching means connects the output port of the amplifier, the other end of the second impedance element and the output terminal together, and for the muting operation, the switching means connects the output port of the amplifier and the other end of one of the second and third impedance elements together, and further connects said output terminal and the other end of the other of the second and third impedance elements together.
  • the entire circuit functions as a non-inverting feedback amplifier.
  • one of the second and third impedance elements which is connected to the output port of the amplifier cooperates with the first impedance element to serve as an attenuator for the output of the amplifier, and the attenuated signal is further attenuated by an attenuator made of the other of the second and third impedance elements and a load impedance to provide a greatly decreased output at said output terminal.
  • the amplifier operates as a noninverting feedback amplifier whenever the circuit performs either the amplification operation or the muting operation.
  • the non-inverting input port is always kept free to receive the input signal.
  • the input bias voltage of the amplifier does not change. Further, when either the amplification function or the muting function is performed, the second or third impedance element is connected between said output terminal and the inverting input port of the amplifier. Therefore, the output bias voltage of the circuit does not change greatly. Accordingly, no clicking noise is generated when the function is switched.
  • FIG. 1 is a diagram of a conventional amplifier circuit with a muting function
  • FIG. 2 is a circuit diagram of an embodiment of the present invention
  • FIG. 3 is a circuit diagram for describing the amplifying operation of the invention.
  • FIG. 4 is a circuit diagram for describing the muting operation of the invention.
  • FIG. 5 is a diagram for illustrating a practical integrated circuit structure of the embodiment shown in FIG. 2;
  • FIG. 6 is a circuit diagram of another embodiment of the invention.
  • a conventional amplifier circuit with a muting function is generally provided with a modified non-inverting feedback amplifier.
  • a resistor 12 is connected between an output terminal 4 of an amplifier 1 and an inverting input terminal 3.
  • a series circuit of a resistor 10 and a capacitor 11 is connected between terminal 3 and ground 5.
  • a signal source 6 is connected between a non-inverting input terminal 2 and ground 5.
  • Amplifier 1, resistors 10 and 12, capacitor 11, and signal source 6 constitute a non-inverting feedback amplifier.
  • a muting switch circuit 50 consists of an NPN transistor 7, a control circuit 8, and a switch 9.
  • the collector electrode of the NPN transistor 7 is connected to input terminal 2, the emitter electrode thereof is connected to ground 5, and the base electrode thereof is connected to a control circuit 8 which controls the operation of transistor 7.
  • the circuit 8 When switch 9 is open, the circuit 8 renders transistor 7 non-conductive.
  • the control circuit 8 With the closure of the switch 9, the control circuit 8 renders transistor 7 conductive.
  • the muting operation of the circuit shown in FIG. 1 is attained by closing switch 9.
  • the control circuit 8 operates so that transistor 7 becomes conductive.
  • any signal from the signal source 6 is bypassed to ground 5 through transistor 7.
  • the bias voltage at input terminal 2 is lowered to the collector saturation voltage of transistor 7.
  • This change of the input bias voltage affects the amplifier 1 to cause clicking noise on the output derived from the output terminal 4.
  • the change in the input bias voltage occurs also, when the muting operation is released by opening the switch 9, also causing a clicking noise.
  • a signal from an input signal source 26 is supplied to a non-inverting input port 22 of the amplifier 21.
  • An inverting input port 23 is connected to ground 25 via a series circuit of a resistor 30 of 220 ohms and a capacitor 31 of 22 microfarads, for example.
  • Resistors 32 and 33 (of 22 kiloohms, for example) are connected to the port 23.
  • the other end of the resistor 32 is connected to an output terminal 38 and an output port 24 of the amplifier 21 via a first switch 34.
  • the other end of the resistor 33 is also connected to the port 24 via a second switch 36.
  • switches 34 and 36 are controlled by signals applied to terminals 35 and 37 from a control circuit 28.
  • control circuit 28 In response to the opening of the switch 29, control circuit 28 generates signals at terminals 35 and 37 so that the first switch 34 is closed and the second switch 36 is opened.
  • control circuit 28 With the closure of switch 29, control circuit 28 produces signals at terminals 35 and 37 so that the first switch 34 is opened and the second switch 36 is closed.
  • the change in the d-c bias potentials at the input ports 22 and 23 of the amplifier 21 are very slight between the amplification operation and the muting operation. This is because the switching between the amplifying and muting operations does not affect the circuit condition of the port 22. Also, the change in the d-c bias potential at the output terminal 38 is very slight since the resistor 32 or 33 is always connected between the terminal 38 and the terminal 23. The latter effect can be obtained more reliably by selecting the resistance of resistors 32 and 33 to be equal. As mentioned above, the change of the d-c bias potentials at the ports 22, 23 and the terminal 38 is very little in response to switching between the amplification and muting operations. Therefore, no clicking noise results even though the circuit operation is altered.
  • FIG. 5 is a circuit diagram for a practical circuit structure of the embodiment shown in FIG. 2.
  • identical structural elements to those of FIG. 2 are denoted by the same reference numerals and their descriptions are omitted.
  • Each of the first and second switches 34 and 36 is made of two parallel connected NPN transistors. In each switch, the base electrodes of the two transistors are commonly connected and the collector electrode of each transistor is connected to the emitter electrode of the other.
  • the common base electrodes of switches 34 and 36 are connected to the terminals 35 and 37, respectively.
  • Each of the switches 34 and 36 passes an AC signal such as an audio signal when it is conductive.
  • the switches, made of two parallel connected transistors has the same conductive impedance and the same voltage drop for both positive and negative parts of the AC signal.
  • the control circuit 28 which supplies control signals to the terminals 35, 37, consists of transistors Q 1 to Q 11 , constant-current sources I 1 to I 3 , and a resistor R 1 .
  • the muting switch 29 controls a base current of the transistors Q 1 and Q 6 . If the switch 29 is open, a constant current from the current source I 1 flows into the transistors Q 1 and Q 6 to render them conductive. A current from the current source I 2 flows to ground through transistor Q 1 so as to render the transistors Q 2 to Q 5 non-conductive. As a result, the base electrodes of the transistors in the second switch 36 do not receive any current, so that the second switch 36 is opened.
  • transistor Q 7 is rendered non-conductive.
  • Current from the current source I 3 therefore turns on transistors Q 8 and Q 9 , which in turn, render transistors Q 10 to Q 11 conductive.
  • transistor Q 11 supplies base current to the transistors in the first switch 34 through the terminal 35 so that switch 34 is closed.
  • the entire circuit including the amplifier 21 functions as a non-inverting feedback amplifier to amplify the input signal.
  • the muting switch 29 is closed, thereby grounding the base electrodes of transistors Q 1 and Q 6 , the conductivity of all transistors Q 1 through Q 11 is the opposite of that described above, resulting in current not being supplied to terminal 35 but being supplied to the terminal 37.
  • the states of the two switches 34 and 36 are reversed and the amplifier functions as a muting circuit as shown in FIG. 4.
  • the circuit shown in FIG. 5 may be constructed as a semiconductor integrated circuit.
  • Such integrated circuit includes all the circuit elements other than resistors 30 and 32, capacitor 31, and switch 29.
  • the input signal source 26 and the power supply source Vcc are, of course, added to the integrated circuit.
  • the integrated circuit requires three external terminals 22, 23, and 38, in addition to the external terminals to be connected to the switch 29, the power supply source Vcc, and the ground potential.
  • FIG. 6 shows another embodiment of the invention, in which a resistor 33' always remains connected between the inverting input port 23 and the output port 24 of the amplifier 21.
  • the resistor 33' and the port 24 are connected to a second switch 36'.
  • a resistor 32'10 is connected to a first switch 34'.
  • the output terminal 38 is connected to the switches 34' and 36'.
  • the switches 34' and 36' are controlled by the outputs of the control circuit 28 to switch the connection of the terminal 38.
  • the circuit of FIG. 6 operates in the same manner as the embodiment of FIG. 2.
  • the resistor 33' since the resistor 33' is always connected to the amplifier 21, the operating condition of the amplifier 21 does not change even when any change between the amplification and muting operations is made.
  • the resistance of resistor 32' can be selected irrespective of the operation of the amplifier 21, to obtain a desired attenuation factor.
  • the resistances 32' and 33' should be selected to be equal to minimize the above-mentioned clocking noise.
  • a single power supply source Vcc of positive polarity was used.
  • two power supply sources of positive and negative polarities may be employed with the circuit structure with the feedback capacitor 31 eliminated.

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  • Amplifiers (AREA)
  • Control Of Amplification And Gain Control (AREA)
US06/499,703 1982-05-31 1983-05-31 Switching circuit operable as an amplifier and a muting circuit Expired - Lifetime US4491800A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP57092585A JPS58209210A (ja) 1982-05-31 1982-05-31 増幅器
JP57-92585 1982-05-31

Publications (1)

Publication Number Publication Date
US4491800A true US4491800A (en) 1985-01-01

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Family Applications (1)

Application Number Title Priority Date Filing Date
US06/499,703 Expired - Lifetime US4491800A (en) 1982-05-31 1983-05-31 Switching circuit operable as an amplifier and a muting circuit

Country Status (4)

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US (1) US4491800A (ja)
EP (1) EP0095774B1 (ja)
JP (1) JPS58209210A (ja)
DE (1) DE3380760D1 (ja)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4864155A (en) * 1987-09-04 1989-09-05 Detusche Thomson-Brandt Gmbh Circuitry for suppressing audible noise
US5029005A (en) * 1990-04-25 1991-07-02 Rca Licensing Corporation Apparatus for the muting of an audio power amplifier in a standby mode
US5255094A (en) * 1990-10-10 1993-10-19 Thomson Consumer Electronics, S.A. Muting circuit for eliminating transient signals generated due to power supply turn-on and turn-off
US5483200A (en) * 1993-06-08 1996-01-09 Sharp Kabushiki Kaisha Light-receiving and amplifying device capable of switching between gain levels at high speed and obtaining a sufficient signal-to-noise ratio over a wide range in quantity of incident light
US6049246A (en) * 1998-12-11 2000-04-11 Vivid Semiconductor, Inc. Amplifier offset cancellation using current copier
WO2002013380A2 (en) * 2000-08-04 2002-02-14 Maxim Integrated Products, Inc. Methods and apparatus for muting the output of amplifier circuits
US6448856B2 (en) * 2000-02-04 2002-09-10 Yamaha Corporation Electronic volume circuit
CN102792587A (zh) * 2010-03-30 2012-11-21 德克萨斯仪器股份有限公司 用于放大器的有源静噪方案

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4506381A (en) * 1981-12-29 1985-03-19 Mitsubishi Denki Kabushiki Kaisha Aural transmitter device
US4978926A (en) * 1989-12-21 1990-12-18 Ford Motor Company Audio limiter using voltage multiplexed feedback
US5621359A (en) * 1995-07-27 1997-04-15 Lucent Technologies Inc. Gain selection technique
CN109195067A (zh) * 2018-07-20 2019-01-11 广州市欧智智能科技有限公司 一种静音控制电路

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4034308A (en) * 1976-07-06 1977-07-05 Licentia Patent-Verwaltungs-G.M.B.H. Amplifier with controllable transmission factor and switchable control characteristic
US4099134A (en) * 1976-07-02 1978-07-04 Licentia Patent-Verwaltungs-G.M.B.H. Amplifier with controllable transmission factor and switchable control characteristic

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3505539A (en) * 1966-09-01 1970-04-07 Ibm Low noise gated d.c. amplifier

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4099134A (en) * 1976-07-02 1978-07-04 Licentia Patent-Verwaltungs-G.M.B.H. Amplifier with controllable transmission factor and switchable control characteristic
US4034308A (en) * 1976-07-06 1977-07-05 Licentia Patent-Verwaltungs-G.M.B.H. Amplifier with controllable transmission factor and switchable control characteristic

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4864155A (en) * 1987-09-04 1989-09-05 Detusche Thomson-Brandt Gmbh Circuitry for suppressing audible noise
US5029005A (en) * 1990-04-25 1991-07-02 Rca Licensing Corporation Apparatus for the muting of an audio power amplifier in a standby mode
US5255094A (en) * 1990-10-10 1993-10-19 Thomson Consumer Electronics, S.A. Muting circuit for eliminating transient signals generated due to power supply turn-on and turn-off
US5483200A (en) * 1993-06-08 1996-01-09 Sharp Kabushiki Kaisha Light-receiving and amplifying device capable of switching between gain levels at high speed and obtaining a sufficient signal-to-noise ratio over a wide range in quantity of incident light
US6049246A (en) * 1998-12-11 2000-04-11 Vivid Semiconductor, Inc. Amplifier offset cancellation using current copier
US6448856B2 (en) * 2000-02-04 2002-09-10 Yamaha Corporation Electronic volume circuit
WO2002013380A2 (en) * 2000-08-04 2002-02-14 Maxim Integrated Products, Inc. Methods and apparatus for muting the output of amplifier circuits
WO2002013380A3 (en) * 2000-08-04 2003-01-09 Maxim Integrated Products Methods and apparatus for muting the output of amplifier circuits
CN102792587A (zh) * 2010-03-30 2012-11-21 德克萨斯仪器股份有限公司 用于放大器的有源静噪方案
CN102792587B (zh) * 2010-03-30 2016-08-31 德克萨斯仪器股份有限公司 用于放大器的有源静噪方案

Also Published As

Publication number Publication date
JPS58209210A (ja) 1983-12-06
EP0095774B1 (en) 1989-10-18
EP0095774A2 (en) 1983-12-07
DE3380760D1 (en) 1989-11-23
JPH0223047B2 (ja) 1990-05-22
EP0095774A3 (en) 1986-03-26

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